The operation of motor vehicles by individuals who are chemically impaired by alcohol or another substance is a major safety problem. Many vehicle accidents involve someone that is under the influence of alcohol and, in some cases, individuals who have already been cited or otherwise identified as misusing or abusing alcohol. In addition to putting the impaired driver at an increased risk of injury or death, the operation of a vehicle while under the influence of alcohol often also affects the safety of others, such as the drivers and passengers in other vehicles. In addition to the increased risk of serious bodily injury or death caused by someone who is driving while under the influence of a chemical substance, there is also an increased risk of serious damage to personal and real property, as well as the cost and potential distraction from other needed services associated with the law enforcement and rescue workers that are called upon to respond to such accidents. As used herein, the term vehicle is intended to include any device or structure for transporting persons or things including, without limitation, automobiles, trucks, boats, planes, trains, etc.
Recognizing the seriousness of driving while under the influence, many laws have been written prohibiting such conduct, and providing various methods for dealing with such offenses when they occur. For example, a court or licensing authority may suspend the driving privileges of someone who is convicted of driving while under the influence of alcohol, or may require that a chemical impairment detection device, such as a BAIID (breath alcohol ignition interlock device), be installed in his or her vehicle. Additionally, a state may require repeat offenders to install such devices as a condition of having their license reinstated. Chemical impairment detection devices may also be used in non-vehicular applications to monitor and detect whether someone has improperly or without authorization consumed alcohol or drugs. For example, abstinence from the use of any alcohol may be a condition of a repeat offender's parole, probation, or home confinement.
When an impairment detection and ignition interlock device, also known as a sobriety interlock, is installed in an individual's vehicle, the individual must pass a sobriety test before the vehicle can be started. However, since the use of impairment detection interlocks is normally done outside the presence of law enforcement or any other supervising authority, and since a penalty may be attributed to a failed test, e.g., the vehicle will not start and a condition of parole may be violated, there can be a temptation to tamper with the impairment detectors to attempt to fraudulently affect its results. For example, if the designated tester has been drinking, he or she could ask someone who is sober to take the test for them. Alternatively, an air compressor, balloon, or other like source of forced air may be blown into a sampling device in an attempt to circumvent the interlock. Once such a clean sample is provided, and the vehicle starts, the impaired driver can then drive away. To prevent this from occurring, detection devices need to provide protection against circumventing the device. In particular, it is important to verify that the exhaled breath sample used in the sobriety test is indeed provided by the designated tester.
To validly determine a tester's blood-alcohol content (BAC) from his or her breath, impairment detection devices typically require a “deep-lung” breath sample. In particular, most state laws require a deep lung air sample having a minimum flow volume of 1.2-1.5 liters of air. During such a sample, the air blown into the mouthpiece generally must comprise alveolar air, which occurs when an expiratory breath substantially exhausts the lungs. Breath expired from the upper portions of the respiratory tract does not necessarily have an alcohol level proportional to that of the bloodstream, and could provide an inaccurate reading. Therefore, the breath-sampling or detection system should detect and prevent the processing of shallow exhalations, e.g., when a tester blows only short puffs of air from the upper portions of the respiratory tract. Additionally, impairment detection devices often require a tester to hum as air is expelled from the lungs, in order to verify that the air sample is from a human and not a forced air source. Typically, a tester is required to blow and hum for about 5 seconds in order to substantially exhaust the lungs and provide a deep-lung sample.
Impairment detection devices perform pressure measurements of an expiratory breath sample to ensure that the sample contains the minimum fluid volume required by law. These measurements have typically been accomplished using differential pressure sensors in combination with an amplifier. This measurement scenario has required a number of components, tubing, and gaskets to properly feed the air sample from the air intake tube to the pressure sensors, adding to the cost and complexity of the detection device. This diversion of sample air away from the breath chamber also increases the likelihood of sample air leaking within the device, reducing the ability to measure pressure accurately, and creating a need to use protective coatings on electronic components and printed circuit boards to prevent degradation due to breath condensation.
External moisture and condensation from breath samples can affect the operation and longevity of a detection device. Because these devices are designed to be used before a vehicle is started, in extremely cold weather an impairment detection device will oftentimes be very cold during its initial use. Breathing warm air into a cold device in an attempt to start a vehicle can cause undesirable breath condensation within the device. This condensation can affect the accuracy of the alcohol sensor, leading to a false positive or negative result.
Accordingly, to overcome the above-described problems in impairment detection devices, it is desirable to have an impairment detection device that uses a simplified, low-cost pressure sensor for more accurately measuring the volume of a breath sample. Additionally, it is desirable to have an impairment detection device that can be preheated in cold environments, prior to receiving a breath sample, to prevent breath moisture condensation and promote optimum operation and accuracy of the device. Further, it is desirable to have a device which includes air-tight seals around a breath intake chamber to prevent breath sample air from leaking within the device. Furthermore, it is desirable to have an impairment detection device that detects a hum sound associated with the intake of a breath sample. Additionally, it is desirable to integrate measuring the volume of an air sample, temperature sensing, and hum detection into a unitary breath chamber.